package com.best.CAS;

/**
 * @author Jiang Akang
 * employeeId: BG435424
 * @date 2020/12/6
 **/

import java.util.concurrent.TimeUnit;
import java.util.concurrent.atomic.AtomicReference;
import java.util.concurrent.atomic.AtomicStampedReference;

/**
 * ABA问题的解决 AtomicStampedReference
 */
public class ABADemo {

    static AtomicReference<Integer> atomicReference = new AtomicReference<>(100);

    //初始化值和版本号
    static AtomicStampedReference<Integer> atomicStampedReference = new AtomicStampedReference<>(100, 1);

    public static void main(String[] args) {
        System.out.println("***********************以下是ABA问题的产生**********************");
        new Thread(() -> {
            atomicReference.compareAndSet(100, 101); //100 101 100 即ABA问题，先改为101，然后再改为100
            atomicReference.compareAndSet(101, 100);
        }, "t1").start();

        new Thread(() -> {
            //暂停1秒钟t2线程，保证上面的t1线程完成了一次ABA操作
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(atomicReference.compareAndSet(100, 2019) + "\t" + atomicReference.get());
        }, "t2").start();

        //暂停一会儿线程
        try {
            TimeUnit.SECONDS.sleep(5);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("***********************以下是ABA问题的解决**********************");

        new Thread(() -> {
            int stamp = atomicStampedReference.getStamp();
            System.out.println(Thread.currentThread().getName() + "\t第1次版本号: " + stamp);
            //暂停1秒钟t3线程，让t4线程获取相同的版本号，同一起点
            try {
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            //如果期望的值是100，版本号是atomicStampedReference.getStamp()，就让版本号加1，值改为101
            atomicStampedReference.compareAndSet(100, 101, atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1);
            System.out.println(Thread.currentThread().getName() + "\t第2次版本号: " + atomicStampedReference.getStamp());
            atomicStampedReference.compareAndSet(101, 100, atomicStampedReference.getStamp(), atomicStampedReference.getStamp() + 1);
            System.out.println(Thread.currentThread().getName() + "\t第3次版本号: " + atomicStampedReference.getStamp());
        }, "t3").start();

        new Thread(() -> {
            int stamp = atomicStampedReference.getStamp();
            System.out.println(Thread.currentThread().getName() + "\t第1次版本号: " + stamp);
            //暂停3秒钟t4线程，保证上面的t3线程完成了一次ABA操作
            try {
                TimeUnit.SECONDS.sleep(3);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            boolean result = atomicStampedReference.compareAndSet(100, 2019, stamp, stamp + 1);
            System.out.println(Thread.currentThread().getName() + "\t修改成功否: " + result + "\t当前最新实际版本号: " + atomicStampedReference.getStamp());
            System.out.println(Thread.currentThread().getName() + "\t当前实际最新值: " + atomicStampedReference.getReference());
        }, "t4").start();
    }
}
